1. Field of the Invention
The present invention relates to portable telephone systems and methods for controlling such systems, particularly to telephone systems provided with the capability of periodically notifying a caller terminal of the status of the call destination terminal when the call destination terminal is busy or outside communication range until connection is made possible, and to methods for controlling such portable telephone systems. This application is based on Patent Application No. Hei 8-288290 filed in Japan, the content of which is incorporated herein by reference.
2. Background Art
Recently, portable telephone systems have been introduced as one type of telephone network. These portable telephone systems often employ a cellular format wherein a base station is provided every few kilometers and there are multiple service areas.
According to a conventional technique described in Japanese Patent Application, First Publication No. Hei 4-337951, when a call destination terminal is busy or is outside communication range, a function known as a "camp-on" function is often used, wherein a camp-on registration operation is performed at the caller terminal and the call is automatically returned to the registrant for connection to the call destination terminal when the call destination terminal becomes free or enters communication range. That is, this portable telephone system comprises a plurality of stationary telephones, a plurality of mobile terminals, a wireless control circuit, a wireless base station, and a switchboard having a CPU, a main memory device, a communication circuit, a wireless control circuit and a trunk control circuit. In this system, the switchboard periodically issues a command in order to check whether or not a specified mobile terminal is within range. If there is a response from the specified mobile terminal, the switchboard judges the specified mobile terminal to be within range and finds it to be within range by means of position registration. If a call is sent from another mobile terminal to the specified mobile terminal while the specified mobile terminal is out of range, the other mobile terminal is notified that the specified terminal is out of range by means of a busy tone or a character display, and an out-of-range camp-on registration operation is performed at the other mobile terminal (by dialing or pressing a one-touch function button). The CPU performs an out-of-range camp-on registration and notifies the other mobile terminal of the registration (by a tone or the like). Meanwhile, the CPU periodically ascertains whether or not the specified mobile terminal is within range, and when an in-range notification is received from the specified mobile terminal, the signal is sent to the camp-on registered other mobile terminal, at which point the camp-on registration state is automatically canceled. Thus, since this portable telephone system is capable of automatically discerning from the state of actual absence by means of movement of the terminals, the catch signal in the event of absence is made the same as a busy signal so as to allow the caller terminal to automatically confirm that the call destination terminal is absent, and by making a camp-on registration at this time, the call is returned to the caller terminal when the call destination terminal enters the communication range, thereby preventing errors wherein a call is returned even in the absence of the call destination terminal. Consequently, improved service can be expected with respect to the caller terminal.
However, this system has the drawback that the call is returned only once to the registrant who is the caller under the camp-on function, and if the registrant is away from the portable telephone or cannot answer the telephone when the call is returned, the camp-on function will be canceled after a standard period of time unless the phone is taken off the hook. Thus, if the registrant has not heard the return call, he may remain unaware that the camp-on function has been canceled.
According to another conventional system described in Japanese Patent Application, First Publication No. Sho 64-44659, when the call destination terminal is busy, the number of the caller terminal is stored on the call destination terminal side, so as to allow the called party to return the call to the stored caller number after the terminal has become free. That is, this system employs a telephone equipped with a one-touch call-back function for storing a caller telephone number which is sent from the switchboard when a signal arrives at the call destination terminal, so as to allow the call to be returned later by retrieving the number from memory in a one-touch operation. The system comprises a line control device for sending and receiving signals between a switchboard and telephones, a memory device for storing the caller number sent from the switchboard via the line control device, an operating device for providing instructions to retrieve and call the caller number, a display device for displaying the caller number, and a control device for retrieving a caller number stored in the memory means and calling the specified caller number based on the instructions from the operating device. Consequently, a list of multiple received calls is able to be prepared inside the telephone, and these can be freely retrieved for one-touch call-backs.
This system has the drawback that the call-back function cannot be used when the mobile terminal on the call destination side is out of range. This is because when the call destination terminal is out of range, it is not possible to achieve a connection, so that the telephone number of the caller terminal cannot be stored in the call destination terminal. Additionally, under this call-back function, the caller must simply wait for the called party to finish communicating with the third party and to return the call to the caller terminal. Therefore, even if the caller urgently wishes to contact the called party, the return call will be delayed if the called party decides to postpone the return call.